1. Field of the Invention
This invention relates to a magnetic recording tape, more specifically, to a magnetic recording tape comprising a support and a two-layered magnetic coating formed on one surface thereof.
2. Description of the Prior Art
In recent years, there has been a need for improved quality and higher recording density in magnetic recording tapes for both open reels and cassettes, and investigations to meet this need have resulted in the production of magnetic tapes comprising at least two magnetic layers, which are generally referred to as multilayer coated tapes.
Such tapes are described, for example, in Japanese Patent Publications 2218/62 and 23678/64, Japanese Patent Applications (OPI) 31602/72 (U.S. Pat. No. 3,761,311), 37903/72, 31907/73 (U.S. Pat. No. 3,775,178), and 31804/75, in U.S. Pat. Nos. 2,643,130, 2,647,954, 2,941,901 and 3,676,217, and in West German Patent Publications 1,190,985 and 1,238,072, etc.
The setting of the bias and equalization are of concern with such magnetic tapes. The preset bias is about 100%, which is generally considered the standard bias. In general, magnetic tapes having the standard bias are used by the largest number of people and are of the most easily usable type. These magnetic tapes have the advantage that no special bias setting or the use of an equalizer is required.
The most convenient means for achieving higher recording density is to increase the coercive force of the ferromagnetic iron oxide used in magnetic tapes. However, such tapes are not exchangeable with those having the standard bias as described above, and in order to obtain optimal magnetic tape characteristics, it is necessary for the user to select a bias and equalization conforming to the magnetic tapes used. Not only is there user confusion with regard to the standard bias, chromium dioxide bias and multilayer bias and the choice of the correct bias and equalization, but also these magnetic tapes have poor interchangeability with many tape recorders and tape decks in ordinary use, and are thus difficult to use. For example, conventional two-layered tapes have improved low frequency output, but require special positions with regard to actuating bias and equalization, for example, as shown in Table 1.
TABLE 1 ______________________________________ Bias (%) Equalizer (.mu. .multidot. sec) Type of Magnetic Tape (cf. 1) (cf. 2) ______________________________________ Low noise type 100 120 Fe-Cr type 130 35 - 50 (cf. 3) CrO.sub.2 160 70 ______________________________________ (cf. 1) The bias of the low noise type is taken as the standard (100%). (cf. 2) The time constant (.mu. .multidot. sec) of equalization for the low noise type is taken as the standard (120 .mu. .multidot. sec). Usually, the time constant in the case of a Fe-Cr type magnetic tape is 4 to 60% of the standard value, and the time constant in the case of a CrO.sub.2 type is 50 to 70% of the standard value. (cf. 3) DUAD.RTM. Ferri-Chrome Tape (made by Sony Corporation), and SCOTCH.RTM. Classic Cassette Tape (made by 3M Co., Ltd.) having a magneti coating composed of an upper layer of CrO.sub.2 and a lower layer of maghemite are examples.
Thus, these magnetic tapes cannot be used in the best condition unless tape recorders or tape decks used have the bias and the equalizer positions as shown in Table 1. The tape recorders or tape decks must be selected according to the manufacturers of magnetic recording tapes, and, thus, these magnetic tapes have the defect they are not universal.